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Abstract

Studies indicate that organic forms of trace minerals can improve cow reproductive performance, particularly during periods of stress. However, limited information is available on the effects of organic trace mineral supplementation on bull fertility. The objective of this study was to evaluate the effect of organic versus inorganic trace mineral supplementation on bull semen quality before and after freezing, as measured by computer-assisted sperm analysis (CASA). Angus and Balancer bulls were assigned to inorganic (n = 9) and organic (n = 10) trace mineral treatments, based on initial semen quality, breed, body weight, and age. The bulls were maintained in a dry lot pen and fed mixed grass hay. Three times each week bulls were individually fed a ration containing either inorganic or organic Zn, Cu, Co and Mn trace mineral for 123 d (mid May to mid September). Treatments were supplemental Zn (450 mg/d), Cu (150 mg/d), Co (12 mg/d), Mn (300 mg/d), Se (3 mg/d), and I (5 mg/d) as either inorganic or as a portion of the same levels as organic sources. Starting on day 60, semen was collected by electroejaculation weekly for 9 weeks. Semen was evaluated by CASA for percent motile, progressive and rapid sperm within 5 min of each collection. On collection weeks 1, 4, and 8, sperm was extended, slowly cooled to 4° C, loaded into 0.5 mL straws, and frozen in liquid nitrogen. After thawing, semen was washed to remove extender and then re-suspended in TALP media. Semen was then evaluated using CASA at 0 and 2 h post-thaw. Data were analyzed by dietary treatment, collection week and their interaction, using the mixed procedure of SAS for repeated measures. For sperm motility parameters, no interaction occurred between collection week and dietary treatment, nor was collection week significant (P > 0.05); therefore, data were analyzed for the effects of treatment on sperm motility parameters, with weekly collections as repeated measures over time. At collection, motile (69.1 vs. 55.2%) and progressive (50.3 vs. 38.5%) sperm were greater (P < 0.05) for bulls receiving the organic trace mineral supplementation compared with bulls receiving the inorganic trace mineral supplementation. Likewise, progressive sperm were improved (P = 0.004) for bulls receiving organic (70.0%) compared with inorganic (55.4%) trace mineral supplementation. The percentage of motile sperm with rapid motility (path velocity > 50 µm/sec) was also greater (P = 0.002) for bulls supplemented with organic compared with inorganic trace mineral (50.7 and 38.0%, respectively). After thawing, motile (16.3 and 7.9%) and progressive (8.9 and 4.1%) sperm were also greater (P < 0.05) for semen from bulls in the organic compared with inorganic trace mineral treatments, respectively. At 2 h post-thaw, motile sperm remained greater (8.5 and 3.7%; P < 0.05), but progressive sperm (4.2 and 1.7%) was similar (P > 0.05) for the organic and inorganic trace mineral treatments, respectively. Sperm motility is the single most important semen quality parameter influencing bull fertility. These results indicated organic trace mineral supplementation improved bull semen quality both before and after freezing. Additional studies are needed to determine if this improvement in semen quality translates into higher pregnancy rates.